Zellweger and Nicole Kidman were highly rumored for the version that was supposed to star Hugh Jackman and (or?) Russell Crowe. I know people hate her around here, but Zellweger would have been fantastic.
I like the idea of Rachel McAdams, and the Deadline article mentions Joseph Gordon-Levitt and Channing Tatum as potential leads, so Ryan Gosling might not be an issue. I'd also wouldn't be surprised if Kate Hudson is in the running. My top pick would be Kristen Wiig, followed by Kate Winslet.
I wonder if at this point Anne Hathaway is even interested in a role like Sarah Brown. It's certainly an iconic role in an iconic show, but she might be a little bored of playing the ingenue now that she's an Oscar winner. I'd see them going after people like Amanda Seyfried, Mia Wasikowswa, Rebecca Hall, and Anna Kendrick.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"